Intra-oral X-ray images are taken by using an X-ray examination apparatus which typically includes, on the one hand, a multi-jointed arm construction and a radiation source arranged in connection with it and, on the other hand, an image-data receiving means to be positioned within the patient's mouth in a desired orientation. Generally, electric imaging sensors, which are based on e.g. charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) technologies, have increasingly emerged along with the use of traditional film.
In order to enable electric intra-oral imaging, one should be able to, for the first, supply the operating power required by the sensor to be positioned within the mouth and, for the second, transfer the image data detected by the sensor to storage or e.g. onto a display. Furthermore, one must be able to identify in some way the moment of beginning of the imaging at least, i.e., the beginning of irradiation. In the earliest electric intra-oral X-ray arrangements cords were used not only for supplying electric energy but also, inter alia, for transmitting signals for synchronising operations of the radiation source and the sensor. Since, solutions have been developed in which e.g. the beginning of irradiation may be identified based on a signal received directly from the sensor, whereby the synchronisation of the operations of the sensor and the radiation source via a cable has not been necessary any more. However, the sensor cable was still required for, on the first hand, supplying electric power and, on the other hand, e.g. transmitting image data and sensor control information.
In intra-oral X-ray imaging, the sensor has to be repeatedly positioned into different positions within the patient's mouth. In this context the sensor cord bends, whereby the cord itself and its connection to the sensor are repeatedly subject to such forces, which will readily wear out the cord and especially its connection to the sensor. It is quite typical that the lifetime of the cord will be shorter than the one of the sensor itself. Although in intra-oral imaging arrangements the cord as such may, when arranged to be of suitable length, provide a safety means for lessening the possibility of the relatively expensive sensor dropping onto the floor and thus getting broken, one has begun in the field of intra-oral X-ray imaging, as there has been done in many other fields as well, developing solutions based on wireless technology.
From the viewpoint of the practical realisation of a wireless intra-oral sensor, an essential characteristic of the sensor is its low power consumption. As it earlier has been possible to achieve diagnostically adequate image quality only with CCD sensor technology, characteristic features of which being fairly high power consumption and complex electronics—not the least because of the several different voltage levels required, a wireless intra-oral X-ray arrangement was not possible to be realised in practice until development of other technologies, such as CMOS sensors, had reached a sufficiently high level.
A limiting condition of intra-oral X-ray imaging is also the sensor size which cannot, for understandable reasons, be very large both for its surface area and its thickness. On the first hand, one must be able to supply in any case the operating power required by the sensor positioned within the patient's mouth and, on the other hand, transfer the image information detected by the sensor to a display or for storage. In addition, it would be preferable if one would be able to transmit e.g. control signals in the direction of the sensor.
Thus, in the electric intra-oral sensors of the first-generation the transfer of data and power was realised via cables, as the technology was not advanced enough for wireless data transmission or, overall, for using wireless technology. Wireless arrangements developed since are typically based on using such a base station in which a battery or a capacitor arranged to the sensor is charged either via a physical electric connection to be arranged between the base station and the sensor or by means of induction current. Also replaceable batteries may be used in the sensors. At least a radio frequency (RF) link has been used for transmitting data from the sensor. As far as these prior art solutions are concerned, a reference may be made to e.g. specification U.S. Pat. No. 6,527,442 and Japanese published application 2003-79617. The latter of these, for example, describes an imaging arrangement intended to be used in intra-oral X-ray imaging in which a battery or a rechargeable battery, used as the power source of the sensor, is placed in a holder unit outside the sensor, which holder unit is connected to the sensor via a cord. The rechargeable battery may be charged in the base station of the holder unit. Image data may be transmitted from the sensor via the holder unit either when it is connected to its base station or wirelessly by radio technology. The wireless data transmission may be arranged either between the sensor and the base station, or to occur directly together with a personal computer e.g. by Bluetooth technology. If the battery can be realised small enough, it may be placed within the sensor, too.
Wireless digital intra-oral sensors on the market today have certain characteristics which would be nice to get rid of or be able to be improved. For the first, using batteries as power source of the sensor causes, besides the bother and cost of changing the battery from time to time, also the fact that it is almost impossible, in practice, to arrange the sensor hermetically sealable in order to enable its cold-sterilisation (immersing it into a liquid). For the second, when using e.g. a rechargeable battery or a capacitor, they must be regularly re-charged before an imaging event, or between them. Here one may find oneself in situations in which charging up must be waited for—especially when the imaging arrangement should, for reasons of radiation hygiene to begin with, be realised such that the imaging cannot be initiated even, if it is possible that the energy stored in the sensor is not enough for being certain that the picture can be taken and either saved in the sensor itself or sent forward.
The small sensor size required in intra-oral imaging is problematic also from the viewpoint of wireless data transmission, because RF links realisable with current technology that would enable quick enough transmission of image information and especially bidirectional data transmission are relatively large and require reasonably much power. Using bidirectional RF links also requisites reasonably complicated electronics. On the other hand, if data transmission from the sensor is arranged only unidirectional, e.g. by sending image information from the sensor to the receiver in real time, re-transmitting the image is not possible in case needed but one has to simply trust that there are no disturbances in the data transmission. In data transmission realised by radio frequencies, disturbances may be caused by e.g. the lengthy data transmission distance from the sensor in the patient's mouth (through soft tissue) to the receiver and both GSM phones and other radio transmitters operating at high frequencies (>10 MHz) (Bluetooth, WLAN) or other radio-frequency devices of high-power. In case the power of the power source is not, for some reason, sufficient for performing the imaging event as a whole and transmission of image data is only possible in real time, one may have to repeat the whole imaging.
There may be a need to use a plurality of sensors in the same premises. When using radio frequencies, one might have to use e.g. different frequencies or one has to arrange selectable transmission channels to the sensors for realising undisturbed data transmission. Even then one must in any case be able to manage in some manner which frequency or channel can be used at a given time.
An object of the present invention, with its preferable embodiments, is thus to offer possibilities for decreasing or avoiding many of the above-described problems and limitations. Especially, an object of the invention is to decrease the problems related to wireless intra-oral imaging based on use of batteries, on one hand, and on sensors to be charged beforehand for imaging, on the other.